[dm-devel] [PATCH 08/10] dm-integrity: add a bitmap mode
Mike Snitzer
snitzer at redhat.com
Wed May 8 17:25:33 UTC 2019
On Wed, May 08 2019 at 12:46pm -0400,
Mikulas Patocka <mpatocka at redhat.com> wrote:
>
>
> On Tue, 7 May 2019, Mike Snitzer wrote:
>
> > On Mon, Apr 29 2019 at 8:57am -0400,
> > Mikulas Patocka <mpatocka at redhat.com> wrote:
> >
> > > Add a new bitmap mode for dm-integrity.
> > >
> > > Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> >
> > This patch header needs much more detail.
> >
> > Can you please be as informative and detailed as possible about what
> > this new bitmap mode is (what constraints it has, where it is expected
> > to be useful, etc)? Also, if you have them, provide some benchmarks
> > that showcase its benefits.
> >
> > Thanks,
> > Mike
>
> The patch adds the documentation to the file
> "Documentation/device-mapper/dm-integrity.txt", so it can be also used as
> a patch header. For example:
>
> "This patch introduces an alternative mode of operation whete dm-integrity
> uses bitmap instead of a journal. If a bit in the bitmap is 1, the
> corresponding region's data and integrity tags are not synchronized - if
> the machine crashes, the unsynchronized regions will be recalculated. The
> bitmap mode is faster than the journal mode, because we don't have to
> write the data twice, but it is also less reliable, because if data
> corruption happens when the machine crashes, it may not be detected."
>
> Benchmark - on an SSD connected to a SATA300 port, when doing large linear
> writes with dd.
>
> buffered I/O:
> raw device throughput - 245MB/s
> dm-integrity with journaling - 120MB/s
> dm-integrity with bitmap - 238MB/s
>
> direct I/O with 1MB block size:
> raw device throughput - 248MB/s
> dm-integrity with journaling - 123MB/s
> dm-integrity with bitmap - 223MB/s
Great, thanks.
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